Chemistry 12 Chapter 2 Exemplar Solutions Question and Answer Part 7

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V. Assertion and Reason Type

Note: In the following questions a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.

(i) Assertion and reason both are correct statements and reason is correct explanation for assertion.

(ii) Assertion and reason both are correct statements but reason is not correct explanation for assertion.

(iii) Assertion is correct statement but reason is wrong statement.

(iv) Assertion and reason both are incorrect statements.

(v) Assertion is wrong statement but reason is correct statement.

Question 51:

Assertion: Molarity of a solution in liquid state changes with temperature.

Reason: The volume of a solution changes with change in temperature.

Answer:

Question 52:

Assertion: When methyl alcohol is added to water, boiling point of water increases.

Reason: When a volatile solute is added to a volatile solvent elevation in boiling point is observed.

Answer:

Question 53:

Assertion: When is added to water a depression in freezing point is observed.

Reason: The lowering of vapour pressure of a solution causes depression in the freezing point.

Answer:

Question 54:

Assertion: When a solution is separated from the pure solvent by a semipermeable membrane, the solvent molecules pass through it from pure solvent side to the solution side.

Reason: Diffusion of solvent occurs from a region of high concentration solution to a region of low concentration solution.

Answer:

VI. Long Answer Type

Question 55:

Define the following modes of expressing the concentration of a solution. Which of these modes are independent of temperature and why?

(i) w/w (mass percentage)

(ii) V/V (volume percentage)

(iii) w/V (mass by volume percentage)

(iv) ppm. (Parts per million)

(v) x (mole fraction)

(vi) M (Molarity)

(vii) m (Molality)

Answer:

Refer to NCERT textbook for Class XII.

Question 56:

Using Raoult’s law explains how the total vapour pressure over the solution is related to mole fraction of components in the following solutions.

(i)

(ii) and

Answer:

Hint: Discuss the following formulas

(i) For a binary solution having both components as volatile liquids, the total pressure will be

total vapour pressure

partial vapour pressure of component

partial vapour pressure of component .

(ii) For a solution containing non-volatile solute, the Raoult’s law is applicable only to vaporisable component (1) and total vapour pressure is written as

Question 57:

Explain the terms ideal and non-ideal solutions in the light of forces of interactions operating between molecules in liquid solutions.

Answer:

Refer to page 45 of NCERT textbook for Class XII.

Question 58:

Why is it not possible to obtain pure ethanol by fractional distillation? What general name is given to binary mixtures which show deviation from Raoult’s law and whose components cannot be separated by fractional distillation. How many types of such mixtures are there?

Answer:

See page 46 of NCERT textbook for Class XII

Question 59:

When kept in water, raisin swells in size. Name and explain the phenomenon involved with the help of a diagram. Give three applications of the phenomenon.

Answer:

[Hint: Explain it with the help of a diagram (Fig. 2.3) illustrating the osmosis of water into raisin.]

Illustrating

Illustrating

Question 60:

Discuss biological and industrial importance of osmosis.

Answer:

Hint: The process of osmosis is of immense biological and industrial importance as is evident from the following examples :

(i) Movement of water from soil into plant roots and subsequently into upper portion of the plant is partly due to osmosis.

(ii) Preservation of meat against bacterial action by adding salt.

(iii) Preservation of fruits against bacterial action by adding sugar. Bacterium in canned fruit loses water through the process of osmosis, shrivels and dies.

(iv) Reverse osmosis is used for desalination of water.

Question 61:

How can you remove the hard calcium carbonate layer of the egg without damaging its semipermeable membrane? Can this egg be inserted into a bottle with a narrow neck without distorting its shape? Explain the process involved.

Answer:

Hint:

Calcium carbonate layer

Calcium Carbonate Layer

Question 62:

Why is the mass determined by measuring a colligative property in case of some solutes abnormal? Discuss it with the help of Van’t Hoff factor

Answer:

Certain compounds when dissolved in suitable solvents either dissociate or associate.

For example ethanoic acid dimerises in benzene due to hydrogen bonding, while in water, it dissociates and forms ions. As a result the number of chemical species in solution increases or decreases as compared to the number of chemical species of solute added to form the solution. Since the magnitude of colligative property depends on the number of solute particles, it is expected that the molar mass determined on the basis of colligative properties will be either higher or lower than the expected value or the normal value and is called abnormal molar mass.

In order to account for the extent of dissociation or association of molecules in solution, Van’t Hoff introduced a factor, i, known as the Van’t Hoff factor. It can be defined as follows.

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